The work of specifying the mobile communication technology Evolved Universal Terrestrial Radio Access Network, E-UTRAN, consisting of the Long Term Evolution, LTE, and System Architecture Evolution, SAE, concepts is currently ongoing within the 3rd Generation Partnership Project, 3GPP. The result of these work items are the specifications on which the E-UTRAN and the Evolved Packet Core, EPC, are built. The E-UTRAN and the EPC together build a so called Evolved Packet System, EPS, network. The general architecture of the EPS network is shown in FIG. 1. The EPS comprises the E-UTRAN which comprises eNodeBs 110. X2 symbolizes logical communication interfaces between the eNodeBs 110. The EPS further comprises Mobile Management Entities, MMEs, and Service Gateways, S-GW 120 for handling data and control signaling exchanged in the EPS. S1 symbolizes logical communication interfaces between the eNodeBs 110 and the MME. The S-GW may be arranged in the same unit as the MME, then called a MME/S-GW 120.
A Public Warning System, PWS, is a system that provides a service that allows the communication network, e.g. EPS network, to distribute warning messages on behalf of a public authority, such as warnings of tsunamis, hurricanes or earthquakes. This ensures that the public has the capability to receive timely and accurate alerts, warnings and critical information regarding disasters and other emergencies. The E-UTRAN performs scheduling and broadcasting of the warning message content received from a Cell Broadcast Center, CBC, of the PWS system. The warning message content is forwarded to the E-UTRAN by the MME. The warning message itself is then broadcasted in dedicated system information blocks from the eNodeB to user equipments, UEs, of the users. The UE may be any wireless communication device, such as a mobile phone, a laptop, a palmtop, a computer etc.
A PWS architecture is shown in FIG. 2. The CBC 130 is part of the core network and connected to the MME 120 via a SBc reference point interface. Further, there is a node called Cell Broadcast Entity, CBE 140 connected to the CBC 130.
3GPP TS 23.041 version 12.1.0, section 9.1.3.4.2 shows a warning message delivery procedure according to the prior art. This procedure is also shown in FIG. 3, which is hereinafter referred to. The procedure is preceded by a registration procedure 1.0 in which a UE 100 (or actually many UEs) registers to the network. Thereafter, the CBE 140, which may be e.g. an information source such as public safety answering point, PSAP, sends emergency information in an emergency broadcast request 1.1 such as “warning type”, “warning message”, “impacted area”, “time period” to the CBC 130. Using the “impacted area” information, the CBC identifies which MMEs need to be contacted and determines the information to be placed into a Warning Area Information Element. The CBC sends a Write-Replace Warning Request message 1.2 containing the warning message to be broadcast and delivery attributes, e.g. Message identifier, Serial Number, Tracking Area ID, TAI, list, Warning Area, etc. The MME uses the TAI list for selecting which eNodeBs to forward the Write-Replace Warning Request message to. The Warning Area may be a list of Cell IDs and/or a list of TAIs and/or one or more Emergency Area IDs. The eNodeB is configured with the TAI(s) and Cell ID(s) it serves and the Emergency Area ID(s) that it belongs to. The eNodeB checks for any match of the contents of the Warning Area with these IDs to identify the cells where to distribute the warning message.
Thereafter, the MME 120 sends a Write-Replace Warning Confirm message 1.3 that indicates to the CBC 130 that the MME has started to distribute the warning message to eNodeBs 110. Upon reception of the Write-Replace Confirm messages 1.3 from the MMEs, the CBC may confirm 1.4 to the CBE 140 that it has started to distribute the warning message. The MME 120 then forwards 1.5 the Write-Replace Warning Request message to the eNodeBs 110. The MME uses the Tracking Area ID list to determine the eNodeBs in the delivery area. If the Tracking Area ID list is empty the message is forwarded to all eNodeBs that are connected to the MME. The eNodeB is to use the Warning Area information to determine the cell(s) in which the message is to be broadcast. The eNodeB returns a Write-Replace Warning Response message 1.7 to the MME.
The eNodeB broadcasts 1.6 the message according to the attributes set by the CBC that originated the warning message distribution. When the UE receives the warning message it can use different warning type values such as: ‘earthquake’, ‘tsunami’ or ‘earthquake and tsunami’, immediately to alert the user 1.8. From the Write-Replace Warning Response messages returned by eNodeBs, the MME determines the success or failure of the delivery and creates a trace record 1.10.
A problem with the procedure described above is that an eNodeB that is restarted will lose the information of ongoing warning broadcasts and will not transmit the information. Such a restarted eNodeB will also miss information of ongoing warning broadcasts sent from the CBC during the time it is being restarted. Hence, users connected to, or camping on, cells belonging to this eNodeB will not receive the information and the CBC is not aware of that the eNodeB has lost this information. Also, an eNodeB newly added to the network in an area with ongoing warning broadcasts do not have the right information to broadcast. Also in this case the CBC does not know that a new eNodeB that should perform broadcast has been added. In other words, there is a risk that users in an area which is soon to suffer from a natural catastrophe is not informed of the approaching danger even though the information is present, which may result in unnecessary human suffering.